Greenland may be ice-free in future if greenhouse gas emissions are not cut significantly, warn researchers

The study cautions that if emissions remain on their current path, the melting ice from Greenland alone could contribute as much as 24 feet to global sea level rise by the year 3000, which would put much of San Francisco, Los Angeles, New Orleans and other cities under water


                            Greenland may be ice-free in future if greenhouse gas emissions are not cut significantly, warn researchers

Greenland could be ice-free in the future if global greenhouse gas emissions are not reduced substantially, warn scientists. Greenland's ice sheet is vast, spanning over 660,000 square miles. It is almost the size of Alaska and 80% as big as the U.S., east of the Mississippi River. Today, the ice sheet covers 81% of Greenland and contains 8% of Earth's fresh water.

A new study, published in Science Advances, says that If worldwide greenhouse gas emissions remain on their current trajectory, Greenland may be ice-free by the year 3000. The researchers caution that if emissions are not reduced, the melting ice from Greenland alone could contribute as much as 24 feet to global sea level rise by the year 3000, which would put much of San Francisco, Los Angeles, New Orleans and other cities under water.

However, the researchers say, if greenhouse gas emissions are cut significantly, the picture will change. Instead of by 3000, Greenland may lose 8% to 25% of ice and contribute up to approximately 6.5 feet of sea level rise. "How Greenland will look in the future - in a couple of hundred years or 1,000 years - whether there will be Greenland, or at least a Greenland similar to today, it's up to us," said Andy Aschwanden, a research associate professor at the University of Alaska Fairbanks Geophysical Institute, in a statement.

Even by the end of the century, the island could lose 4.5% of its ice, contributing up to 13 inches of sea level rise, the researchers add. The team comprised researchers from the University of Alaska Fairbanks, Fairbanks; University of Missoula, USA; Danish Meteorological Institute, Copenhagen, Denmark; and DTU Space, Denmark.

"The Greenland Ice Sheet holds 7.2 m of sea level equivalent, and in recent decades, rising temperatures have led to accelerated mass loss. We find that Greenland could contribute 5 to 33 cm to sea level by 2100, with discharge from outlet glaciers contributing 8 to 45% of the total mass loss. Our analysis shows that uncertainties in projecting mass loss are dominated by uncertainties in climate scenarios and surface processes, whereas uncertainties in calving and frontal melt play a minor role. We project that Greenland will very likely become ice-free within a millennium without substantial reductions in greenhouse gas emissions," said the paper. 

The researchers ran 500 simulations for multiple three climate scenarios using the "Parallel Ice Sheet Model", developed at the Geophysical Institute, to create a picture of how Greenland's ice would respond to different climate scenarios. The model included parameters on the ocean and atmospheric conditions as well as ice geometry, flow and thickness.

These maps of Greenland show ice losses under two 'representative concentration pathways (RCPs)' of greenhouse gases in Earth's atmosphere from present day to the year 3000. The RCPs, adopted by the Intergovernmental Panel on Climate Change, reflect higher (8.5) and lower (2.6) greenhouse gas concentrations associated with different levels of emissions from human use of fossil fuels. Currently, the planet is on the higher pathway. (UAF Geophysical Institute)

"In a thousand years, the Greenland Ice Sheet will look significantly different than today. Depending on the emission scenario, the Greenland Ice Sheet will have lost 8 to 25% (under the best possible scenario), 26 to 57% (under moderate scenario), or 72 to 100% (in the worst case scenario) of its present-day mass, contributing 0.59 to 1.88 m, 1.86 to 4.17 m, or 5.23 to 7.28 m to global mean sea level, respectively," the paper stated.

Simulating ice sheet behavior is difficult because the retreat of outlet glaciers leads to ice loss. These glaciers, at the margins of ice sheets, drain the ice from the interior like rivers, often in troughs hidden under the ice itself.

"This study is the first model to include these outlet glaciers. It found that their discharge could contribute as much as 45% of the total mass of ice lost in Greenland by 2200. Outlet glaciers are in contact with water, and water makes ice melt faster than contact with air, like thawing a chicken in the sink. The more ice touches water, the faster it melts. This creates a feedback loop that dramatically affects the ice sheet. However, to simulate how the ice flows, the scientists need to know how thick the ice is," said the findings.

The team used data from a NASA airborne science campaign called "Operation IceBridge." The latter uses aircraft equipped with a full suite of scientific instruments, including three types of radar that can measure the ice surface, the individual layers within the ice and penetrate to the bedrock to collect data about the land beneath the ice.

On average, Greenland's ice sheet is 1.6 miles thick, but there is a lot of variation depending on where one measures. Because previous research results lacked these details, scientists could not simulate present-day conditions as accurately, which makes it more difficult to predict what will happen in the future.

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